1. Field of the Invention
The invention relates to an electro-optical measuring instrument for detecting the relative position assumed by two bodies or two surfaces of bodies with respect to one another.
Known instruments of this type are fitted with a measuring arrangement which has at least one light beam transmitter and at least one single-axis or multi-axis optoelectronic position detector. In a path fixed with respect to one body or surface region the light beam transmitter of this measuring arrangement directs a focused light beam of small divergence, for example a laser beam, directly or via a mirror arrangement belonging to the measuring arrangement onto the light-sensitive measuring surface of the position detector, which in the case of direct irradiation from the light transmitter is located on the other body, and in the case of reflection from the mirror arrangement fastened to the other body is located on the same body as the light beam transmitter. The position detector supplies electrical signals corresponding to the coordinates of the instantaneous point of impingement of the light beam on the measuring surface, and the measuring arrangement or parts of the latter are configured such that it/they can be displaced in a defined measuring movement with the or on the one and/or other body or surface region in such a way that the geometrical locus, produced in the course of the measuring movement, of the points of impingement of the light beam on the measuring surface is in a predetermined relationship to the relative position of the bodies or surface regions to be determined. The measuring instrument can therefore calculate under programmed control the relative position to be detected, on the basis of the electric signals supplied during the measuring movement. Electro-optical measuring instruments of this known category are disclosed, inter alia, by EP 0 474 799 B1 and DE 39 11 307 A1 of the Applicant.
2. Description of Related Art
The measuring instruments of the generic type according to the abovementioned printed publications are used to detect the state of alignment of shafts, for example shafts which are to be coupled to one another and belong to two rotary machines, for example a motor and an electric generator driven thereby, so that positional corrections can be undertaken in the event of a deviation from the ideal state of alignment which exceeds a predetermined permissible size, before, for example, the shaft bearings and/or the shaft coupling suffer damage caused by the defective alignment.
If the alignment error is very large, it can happen when working with the known measuring instruments that the laser beam impinges on the measuring surface of the position detector, which surface has a prescribed size, only over subregions of the measuring movement. So far, it has been the approach in such cases initially to undertake, more or less by eye and on the basis of the incompletely obtained measuring signals, one or more preliminary corrections of the relative position of the shafts until the existing alignment error has been reduced to a measure at which the point of impingement of the light beam has remained on the measuring surface of the position detector in the course of the subsequent measuring movements beyond the complete measuring movement in each case, thus rendering it possible to undertake exact corrections purposefully from then on.
Comparable situations can also arise in the case of other measuring instruments of the generic type which are used, for example, to measure the shape of a surface to be measured with respect to a plane defined by the light beam or laser beam.